The present invention relates generally to a network interface module and method of operation, and more particularly to an interface board and software for connecting a broad range of computer systems to a real time local area network.
It was decided that a local area network (LAN) should be used to solve problems associated with coupling a mainframe computer system to cockpits, etc in real-time pilot-in-the-loop aircraft simulation. The pilots participate in these simulations in cockpits that are located throughout the facility. Other equipment necessary to the simulation is also located at a considerable distance from the mainframe system. The mainframe system must not only run the simulation program, but must also calculate all the parameters to control these cockpits and equipment. The control parameters must then be output on more than one hundred analog and digital control lines. Information from the cockpits and equipment is also gathered by inputting many other analog and digital control lines.
Several problems with this method of operation can be seen immediately. The first is that the mainframe system is performing hundreds of input/output instructions in order to control cockpits and other equipment, instead of working on the simulation program. This means that as new equipment and more sophisticated cockpits are added, there is less memory and less computing power left in the mainframe system with which to accomplish the simulation program. Also, since the cockpits and other equipment are located at a considerable distance from the mainframe system, all analog lines can pick up a noticeable amount of electrical noise. Another problem occurs when new equipment or a cockpit is added to the simulation system. This is the adding of a hundred or more control lines that must be placed between the new item and the mainframe system. A special interface may be necessary for a new piece of equipment, if it is not directly compatible with the mainframe system.
To correct some of the problems mentioned above, it was decided to place small computer systems at every cockpit and at each piece of equipment. These "smart" interfaces would offload the computations and input/output operations from the mainframe system. This would leave the mainframe system free to do more work on the simulation programs themselves. However, the mainframe system must still have some method for communicating with these "smart" interfaces. It was decided that a digital, real time, standard Local Area Network (LAN) would be employed to handle communications. This in itself presented several problems. One was that not all of the "smart" interfaces would be identical systems and many of them had no "off the shelf" interface to a LAN. Also, the "off-the-shelf" interfaces that were available were usually not meant to be used as interfaces to a real-time LAN. Because of this, the software overhead used to invoke communications was often too slow to meet the real-time requirements.
It was desirable to have a network interface module that could be easily connected to any computer and not be dependent on any one system or one type of computer bus. It would also meet all standards for transmission and reception of frames of data, and would be able to transmit and receive these frames of data fast enough to meet the real-time requirements. This meant that the software to invoke communications with the interface module had to be the bare minimum necessary to get a block of data back and forth between the "smart" interface and the mainframe system.
United States patents of interest include U.S. Pat. No. 4,280,285 to Haas, which shows in FIG. 1 an interface circuit 72 for connecting an master controller 74 to a memory 70 and computer 68. The interface is used in conjunction with an aircraft simulator 50 having a cockpit 52. The signals pass through an instructor station 76 which as described in the patent, is capable of handling up to eight cockpits. Donahue et al in U.S. Pat. No. 4,144,550 show a system with a master interface 4 for connecting a master controller 2 to a passive area controller 6 and an active area controller 12. Daly et al in U.S. Pat. No. 4,071,887 is directed to a bidirectional interface for synchronous data interchange. The patented system allows data transfer between serial data channels and the parallel bidiredctional data bus of a microprocessor. U.S. Pat. No. 3,988,716 to Anderson is concerned with an interface logic circuit which permits the transfer of information between two computers which permits the transfer of information between two computers having asynchronous clocks. Munter in U.S. Pat. No. 4,154,985 discloses an interface circuity for coupling a data signal from one digital telephone facility, operating at one data rate, to another d1gital telephone facility operating at another data bit rate. The patented interface circuit includes storage and a frequency converter. Suhonick in U.S. Pat. No. 4,549,275 shows a graphics data handling system wherein a work station cooperates with a host computer which stores a list representation of complex three dimensional structure. Schwan et al in U.S. Pat. No. 4,604,682 disclose a buffer system for interfacing a data processor to a communications system using a buffer memory for storing input and output data. However, none of these references teach how to solve the problem of providing an interface circuit for matching a real time cockpit display graphics processor to a minicomputer.